1. Field of the Invention
The present invention relates to a thermosetting resin composition, and more particularly to a thermosetting resin composition excellent in processability, heat resistance and adhesive property.
2. Description of the Prior Art
Thermosetting resins are used as materials for casting, impregnation, lamination and molding in the fields of electrical insulation, construction, etc. In these fields, there is a current tendency that the conditions under which these materials are used become more and more severe. Particularly, an increasing importance is being attached to heat resistance of material.
Hitherto, thermosetting polyimide resin and heat resistance epoxy resin have been used for such purposes. Or, as a material capable of replacing them, there was proposed in Japanese Patent Kokai (Laid-Open) No. 154,897/77 a thermosetting mixture comprising a polyimide, an allyl group containing epoxy compound having a special structure and a curing agent.
However, polyimide resin is disadvantageous in that its processing requires a longterm heating at a high temperature, and it is insufficient in adhesive property. Although epoxy resin having an improved heat resistance is excellent in processability and adhesive property, it is also disadvantageous in that it is insufficient in the high-class heat resistance, i.e. mechanical and electrical properties at high temperature, and heat degradation property for long term.
Further, an allyl group-containing epoxy compound used in the thermosetting mixture disclosed in Japanese Patent Kokai (Laid-Open) No. 154,897/77 was prepared by subjecting an allyl ether compound to Claisen rearrangement and then epoxidizing the rearranged product, from which a uniform cured product is difficult to prepare probably because the nucleus-substituting allyl group and epoxy group are located on the ortho positions of one aromatic ring. Particularly in the case of novolac type, this type of composition was inferior in physical property such as electrical insulating property and heat resistance of cured product probably because some of these groups are apt to remain unreacted.
Considering the above-mentioned background, the present inventors conducted earnest studies to find a resin composition having excellent processability, heat resistance and adhesive property, and found that a resin composition comprising a specified resin and a polymaleimide compound is suitable for the above mentioned purpose.
Based on the findings, the present invention was accomplished.
According to the present invention, there is provided a thermosetting resin composition comprising (A) phenol novolac resin some of the hydroxyl groups of which have been allyl-etherified and the other hydroxyl groups have added thereto a compound having one or more epoxy group(s) and (B) a polymaleimide compound having two or more maleimide groups in the molecule.